I think the Ubuntu Software Center is quite demanding in terms of CPU usage and bandwidth. So if you have an low-spec CPU and a slow net you will experience slowness. But 4-5 min does seem too slow. Could you update your question to provide your CPU/RAM and (average) net speed?
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user25656Dec 29 '12 at 16:21

This isn't a real answer. You are assuming that OP his device is slow. And although Synaptic is a handy app, it differs too much from the software center to be a real replacement. And synaptic doesn't offer the same stuff. @Sebastian synaptic is a package manager program, not quite the same as ubuntu software center.
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Dr_BunsenDec 29 '12 at 12:09

@EliahKagan one can, but one will see that it is very different, and one has to know what one wants. Or else one is never going to find what one wants.
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Dr_BunsenDec 29 '12 at 15:59

@Dr_Bunsen Except for paid apps (which you can install but not buy in Synaptic), I don't think this is a realistic problem. It's usually very easy to search for the names of packages if you know some other name that's widely used to describe the software. Since search engines let you start out with even less information, I think many users already search for package names before they install software with USC, and most users who don't would have no trouble doing so. I agree that USC provides distinct advantages and I'm glad we have it, but if it's not working right (e.g., it's very slow)...
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Eliah KaganDec 29 '12 at 16:14